Simple and Versatile 3D Printed Microfluidics Using Fused Filament Fabrication

Microfluidic Chips for Life Sciences-A Comparison of Low Entry Manufacturing Technologies

Microfluidic water-in-oil droplets are a versatile tool for biological and biochemical applications due to the advantages of extremely small monodisperse reaction vessels in the pL-nL range. A key factor for the successful dissemination of this technology to life science laboratory users is the ability to produce microfluidic droplet generators and related accessories by low-entry barrier methods, which enable rapid prototyping and manufacturing of devices with low instrument and material costs. The direct, experimental side-by-side comparison of three commonly used additive manufacturing (AM) methods, namely fused deposition modeling (FDM), inkjet printing (InkJ), and stereolithography (SLA), is reported. As a benchmark, micromilling (MM) is used as an established method. To demonstrate which of these methods can be easily applied by the non-expert to realize applications in topical fields of biochemistry and microbiology, the methods are evaluated with regard to their limits for the minimum structure resolution in all three spatial directions. The suitability of functional SLA and MM chips to replace classic SU-8 prototypes is demonstrated on the basis of representative application cases.

"Learning on a chip:" Microfluidics for formal and informal science education

Microfluidics is a technique for the handling of small volumes of liquids on the order of picoliters to nanoliters and has impact for miniaturized biomedical science and fundamental research. Because of its multi- and interdisciplinary nature (i.e., combining the fields of biology, chemistry, physics, and engineering), microfluidics offers much potential for educational applications, both at the university level as well as primary and secondary education. Microfluidics is also an ideal "tool" to enthuse and educate members of the general public about the interdisciplinary aspects of modern sciences, including concepts of science, technology, engineering, and mathematics subjects such as (bio)engineering, chemistry, and biomedical sciences. Here, we provide an overview of approaches that have been taken to make microfluidics accessible for formal and informal learning. We also point out future avenues and desired developments. At the extreme ends, we can distinguish between projects that teach how to build microfluidic devices vs projects that make various microscopic phenomena (e.g., low Reynolds number hydrodynamics, microbiology) accessible to learners and the general public. Microfluidics also enables educators to make experiments low-cost and scalable, and thereby widely accessible. Our goal for this review is to assist academic researchers working in the field of microfluidics and lab-on-a-chip technologies as well as educators with translating research from the laboratory into the lecture hall, teaching laboratory, or public sphere.

Integrated Printed Microfluidic Biosensors

Integrated printed microfluidic biosensors are one of the most recent point-of-care (POC) sensor developments. Fast turnaround time for production and ease of customization, enabled by the integration of recognition elements and transducers, are key for on-site biosensing for both healthcare and industry and for speeding up translation to real-life applications. Here, we provide an overview of recent progress in printed microfluidics, from the 2D to the 4D level, accompanied by novel sensing element integration. We also explore the latest trends in integrated printed microfluidics for healthcare, especially POC diagnostics, and food safety applications.

New Directions for Artificial Cells Using Prototyped Biosystems

Microfluidics has has enabled the generation of  a range of single compartment and multicompartment vesicles and bilayer-delineated droplets that can be assembled in 2D and 3D. These model systems are becoming increasingly used as artificial cell chassis and as biomimetic constructs for assembling tissue models, engineering therapeutic delivery systems, and screening drugs. One bottleneck in developing this technology is the time, expertise, and equipment required for device fabrication. This has led to interest across the microfluidics community in using rapid prototyping to engineer microfluidic devices from computer-aided-design (CAD) drawings. We highlight how this rapid-prototyping revolution is transforming the fabrication of microfluidic devices for artificial cell construction in bottom-up synthetic biology. We provide an outline of the current landscape and present how advances in the field may give rise to the next generation of multifunctional biodevices, particularly with Industry 4.0 on the horizon. Successfully developing this technology and making it open-source could pave the way for a new generation of citizen-led science, fueling the possibility that the next multibillion-dollar start-up could emerge from an attic or a basement.

3D printing in cell culture systems and medical applications

3D printing plays an important role in various biomedical research applications including, but not limited to, culture systems and implantable devices. In this review, we discuss recent development in the applications of 3D printing technologies for clinically motivated research, particularly focusing on the fabrication of constructs subsequently incorporated with cells. Applications of this technology include pharmaceutical delivery, bioreactor culture platforms, acellular scaffolds, imaging modalities, and organ-on-a chip systems. Emphasis is placed on technological developments not possible without 3D printing technologies: where traditional manufacturing approaches would be cumbersome to demonstrate research objectives. The clinical applications of 3D printing are rapidly moving from the research to production phases and will certainly continue to grow, with ever increasing numbers of therapies becoming commercialized. The work discussed here holds promise for various applications in structural improvements, drug delivery, and physiology research.

3D-printed miniaturized fluidic tools in chemistry and biology

3D printing (3DP), an additive manufacturing (AM) approach allowing for rapid prototyping and decentralized fabrication on-demand, has become a common method for creating parts or whole devices. The wide scope of the AM extends from organized sectors of construction, ornament, medical, and R&D industries to individual explorers attributed to the low cost, high quality printers along with revolutionary tools and polymers. While progress is being made but big manufacturing challenges are still there. Considering the quickly shifting narrative towards miniaturized analytical systems (MAS) we focus on the development/rapid prototyping and manufacturing of MAS with 3DP, and application dependent challenges in engineering designs and choice of the polymeric materials and provide an exhaustive background to the applications of 3DP in biology and chemistry. This will allow readers to perceive the most important features of AM in creating (i) various individual and modular components, and (ii) complete integrated tools.

Automated 4-Sample Protein Immunoassays using 3D-Printed Microfluidics

Low cost, miniaturized assay platforms that work with small sample volumes, high sensitivity and rapid detection will have high value in future biomolecular diagnostics. Herein we report an automated, 3D printed electrochemiluminescent (ECL) immunoarray integrated with a nanostructured pyrolytic graphite sheet (PGS) microwell chip configured to detect 2 proteins simultaneously from complex liquid samples with high sensitivity and selectivity. Assays are done in 18 min at cost of < $1.00 using 1-2 microliters of sample. 3D printed microfluidic array design integrates reagent and sample chambers with rapid ECL detection. A commercial programmable syringe pump used with a preset program allows pump to pause and resume reagent delivery as required for completion of the sandwich immunoassays. Nanostructured surfaces feature antibody-decorated single wall carbon nanotube forests on PGS chip microwells, and sensitivity is amplified via massively labeled RuBPY-silica nanoparticles for detection. Prostate specific antigen (PSA) and prostate specific membrane antigen (PSMA) were measured simultaneously from human serum on the immunoarray with detection limits 150 fg mL^-1 for PSA and 230 fg mL^-1 for PSMA, with dynamic ranges up to 5 ng mL^-1. Validation of the immunoarray by measuring these proteins in human serum showed good correlation with single protein ELISA. These 3D printed platforms can be easily adapted to multiple applications and configurable CAD files for the immunoarray can be downloaded from our lab's website.

Droplet microfluidics for the construction of compartmentalised model membranes

The design of membrane-based constructs with multiple compartments is of increasing importance given their potential applications as microreactors, as artificial cells in synthetic-biology, as simplified cell models, and as drug delivery vehicles. The emergence of droplet microfluidics as a tool for their construction has allowed rapid scale-up in generation throughput, scale-down of size, and control over gross membrane architecture. This is true on several levels: size, level of compartmentalisation and connectivity of compartments can all be programmed to various degrees. This tutorial review explains and explores the reasons behind this. We discuss microfluidic strategies for the generation of a family of compartmentalised systems that have lipid membranes as the basic structural motifs, where droplets are either the fundamental building blocks, or are precursors to the membrane-bound compartments. We examine the key properties associated with these systems (including stability, yield, encapsulation efficiency), discuss relevant device fabrication technologies, and outline the technical challenges. In doing so, we critically review the state-of-play in this rapidly advancing field.

FDM 3D Printing of High-Pressure, Heat-Resistant, Transparent Microfluidic Devices

Transparent surfaces within microfluidic devices are essential for accurate quantification of chemical, biological, and mechanical interactions. Here, we report how to create low-cost, rapid 3D-printed microfluidic devices that are optically free from artifacts and have transparent surfaces suitable for visualizing a variety of fluid phenomenon. The methodology described here can be used for creating high-pressure microfluidic systems (significantly higher than PDMS-glass bonding). We develop methods for annealing Poly-Lactic Acid (PLA) microfluidic devices demonstrating heat resistance typically not achievable with other plastic materials. We show DNA melting and subsequent fluorescent imaging analysis, opening the door to other high-temperature applications. The FDM techniques demonstrated here allow for fabrication of microfluidic devices for precise visualization of interfacial dynamics, whether mixing between two laminar streams or droplet tracking. In addition to these characterizations, we include a printer troubleshooting guide and printing recipes for device fabrication to facilitate FDM printing for microfluidic device development.

Extrusion-Based 3D Printing of Microfluidic Devices for Chemical and Biomedical Applications: A Topical Review

One of the most widespread additive manufacturing (AM) technologies is fused deposition modelling (FDM), also known as fused filament fabrication (FFF) or extrusion-based AM. The main reasons for its success are low costs, very simple machine structure, and a wide variety of available materials. However, one of the main limitations of the process is its accuracy and finishing. In spite of this, FDM is finding more and more applications, including in the world of micro-components. In this world, one of the most interesting topics is represented by microfluidic reactors for chemical and biomedical applications. The present review focusses on this research topic from a process point of view, describing at first the platforms and materials and then deepening the most relevant applications.

3D printing for electroanalysis: From multiuse electrochemical cells to sensors

This work presents potential applications of low-cost fused deposition modeling 3D-printers to fabricate multiuse 3D-printed electrochemical cells for flow or batch measurements as well as the 3D-printing of electrochemical sensing platforms. Electrochemical cells and sensors were printed with acrylonitrile butadiene styrene (ABS) and conductive graphene-doped polylactic acid (G-PLA) filaments, respectively. The overall printing operation time and estimated cost per cell were 6 h and $ 6.00, respectively, while the sensors were printed within minutes (16 sensor strips of 1 × 2 cm in 10 min at a cost of $ 1.00 each sensor). The cell performance is demonstrated for the amperometric detection of tert-butylhydroquinone, dipyrone, dopamine and diclofenac by flow-injection analysis (FIA) and batch-injection analysis (BIA) using different working electrodes, including the proposed 3D-printed sensor, which presented comparable electroanalytical performance with other carbon-based electrodes (LOD of 0.1 μmol L^-1 for dopamine). Raman spectroscopy and scanning electron microscopy of the 3D-printed sensor indicated the presence of graphene nanoribbons within the polymeric matrix. Electrochemical impedance spectroscopy and heterogeneous electron transfer constants (k₀) for the redox probe Ru(NH₃)₆⁺³ revealed that a glassy-carbon electrode presented faster electron transfer rates than the 3D-printed sensor; however, the latter presented lower LOD values for dopamine and catechol probably due to oxygenated functional groups at the G-PLA surface.

Simple, low-cost fabrication of acrylic based droplet microfluidics and its use to generate DNA-coated particles

Hydrogel microparticles were copolymerized with surface-immobilized DNA. Particles derived from a microfluidic device and particles derived from mechanical homogenization were compared. The hypothesis was tested that a controlled droplet generation mechanism would produce more homogeneous particles. Surprisingly, the DNA content of both particle types was similarly inhomogeneous. To make this test possible, a simple, low cost, and rapid method was developed to fabricate a microfluidic chip for droplet generation and in-line polymerization. This method used a low-cost laser cutter ($400) and direct heat bonding (no adhesives or intermediate layers). The flow focusing droplet generator produced droplets and hydrogel particles 10-200 μm in diameter.

Accessing microfluidics through feature-based design software for 3D printing

Additive manufacturing has been a cornerstone of the product development pipeline for decades, playing an essential role in the creation of both functional and cosmetic prototypes. In recent years, the prospects for distributed and open source manufacturing have grown tremendously. This growth has been enabled by an expanding library of printable materials, low-cost printers, and communities dedicated to platform development. The microfluidics community has embraced this opportunity to integrate 3D printing into the suite of manufacturing strategies used to create novel fluidic architectures. The rapid turnaround time and low cost to implement these strategies in the lab makes 3D printing an attractive alternative to conventional micro- and nanofabrication techniques. In this work, the production of multiple microfluidic architectures using a hybrid 3D printing-soft lithography approach is demonstrated and shown to enable rapid device fabrication with channel dimensions that take advantage of laminar flow characteristics. The fabrication process outlined here is underpinned by the implementation of custom design software with an integrated slicer program that replaces less intuitive computer aided design and slicer software tools. Devices are designed in the program by assembling parameterized microfluidic building blocks. The fabrication process and flow control within 3D printed devices were demonstrated with a gradient generator and two droplet generator designs. Precise control over the printing process allowed 3D microfluidics to be printed in a single step by extruding bridge structures to ‘jump-over’ channels in the same plane. This strategy was shown to integrate with conventional nanofabrication strategies to simplify the operation of a platform that incorporates both nanoscale features and 3D printed microfluidics.

High-Content Assessment of Cardiac Function Using Heart-on-a-Chip Devices as Drug Screening Model

Drug discovery and development continues to be a challenge to the pharmaceutical industry despite great advances in cell and molecular biology that allow for the design of better targeted therapeutics. Many potential drug compounds fail during the clinical trial due to inefficacy and toxicity that were not predicted during preclinical stages. The fundamental problem lies with the use of traditional drug screening models that still largely rely on the use of cell lines or animal cell monolayers, which leads to lack of predictive power of human tissue and organ response to the drug candidates. More physiologically relevant systems are therefore critical in relieving the burden of high failure rates. Emerging knowledge and techniques in tissue engineering and microfabrication have enabled the development of micro-engineered systems - collectively known as organs-on-chips - that may lead to a paradigm shift in preclinical drug screening assays. In this review we explore the technological advances and challenges in the development of heart-on-a-chip models, by addressing current assessment methods for drug-induced cardiotoxicity and providing a perspective on the modifications that should be implemented to realize the full potential of this system.

3D-Printing of Functional Biomedical Microdevices via Light- and Extrusion-Based Approaches

3D-printing is a powerful additive manufacturing tool, one that enables fabrication of biomedical devices and systems that would otherwise be challenging to create with more traditional methods such as machining or molding. Many different classes of 3D-printing technologies exist, most notably extrusion-based and light-based 3D-printers, which are popular in consumer markets, with advantages and limitations for each modality. The focus here is primarily on showcasing the ability of these 3D-printing platforms to create different types of functional biomedical microdevices-their advantages and limitations are covered with respect to other classes of 3D-printing, as well as the past, recent, and future efforts to advance the functional microdevice domain. In particular, the fabrication of micromachines/robotics, drug-delivery devices, biosensors, and microfluidics is addressed. The current challenges associated with 3D-printing of functional microdevices are also addressed, as well as future directions to improve both the printing techniques and the performance of the printed products.

One-step volumetric additive manufacturing of complex polymer structures

Two limitations of additive manufacturing methods that arise from layer-based fabrication are slow speed and geometric constraints (which include poor surface quality). Both limitations are overcome in the work reported here, introducing a new volumetric additive fabrication paradigm that produces photopolymer structures with complex nonperiodic three-dimensional geometries on a time scale of seconds. We implement this approach using holographic patterning of light fields, demonstrate the fabrication of a variety of structures, and study the properties of the light patterns and photosensitive resins required for this fabrication approach. The results indicate that low-absorbing resins containing ~0.1% photoinitiator, illuminated at modest powers (~10 to 100 mW), may be successfully used to build full structures in ~1 to 10 s.

Development of a microfluidic platform integrating high-resolution microstructured biomaterials to study cell-material interactions

Microfluidic screening platforms offer new possibilities for performing in vitro cell-based assays with higher throughput and in a setting that has the potential to closely mimic the physiological microenvironment. Integrating functional biomaterials into such platforms is a promising approach to obtain a deeper insight into the interactions occurring at the cell-material interface. The success of such an approach is, however, largely dependent on the ability to miniaturize the biomaterials as well as on the choice of the assay used to study the cell-material interactions. In this work, we developed a microfluidic device, the main component of which is made of a widely used biocompatible polymer, polylactic acid (PLA). This device enabled cell culture under different fluidic regimes, including perfusion and diffusion. Through a combination of photolithography, two-photon polymerization and hot embossing, it was possible to microstructure the surface of the cell culture chamber of the device with highly defined geometrical features. Furthermore, using pyramids with different heights and wall microtopographies as an example, adhesion, morphology and distribution of human MG63 osteosarcoma cells were studied. The results showed that both the height of the topographical features and the microstructural properties of their walls affected cell spreading and distribution. This proof-of-concept study shows that the platform developed here is a useful tool for studying interactions between cells and clinically relevant biomaterials under controlled fluidic regimes.

3D-Printed Microflow Injection Analysis Platform for Online Magnetic Nanoparticle Sorptive Extraction of Antimicrobials in Biological Specimens as a Front End to Liquid Chromatographic Assays

In this work, the concept of 3D-printed microflow injection (3D-μFI) embodying a dedicated multifunctional 3D-printed stator onto a rotary microvalve along with a mesofluidic sample preparation platform is proposed for the first time. A transparent 3D-printed stereolithographic mesofluidic chip device accommodating polyaniline (PANI) decorated magnetic nanoparticles (32.5 ± 3.8 mg) is harnessed to in-line sorptive microextraction as a front end to liquid chromatography with peak focusing. As a proof-of-concept application, the 3D-μFI assembly was resorted to matrix cleanup and automatic programmable-flow determination of organic emerging contaminants (4-hydroxybenzoate analogues and triclosan as antimicrobial model analytes) in human saliva and urine samples. By using a sample volume of 1.0 mL with a loading flow rate of 200 μL min^-1, an eluent volume of 120 μL at 80 μL min^-1, and online HPLC injection of 300 μL of the mixture of eluate and Milli-Q water (in a 1:2 ratio) to prevent band broadening effects of the most polar analytes, the limits of detection (3σ criterion) ranged from 1.1 to 4.5 ng mL^-1 for methylparaben (MP), ethylparaben (EP), propylparaben (PrP), phenylparaben (PhP), butylparaben (BP), and triclosan (TCS). Enhancement factors of 16-25 were obtained for the target analytes. Spike recoveries ranged from 84 to 117% for both saliva and urine samples. The online 3D-μFI hyphenated method is synchronized with the chromatographic separation and features a chip lifetime of more than 20 injections with minimal losses of moderately nonpolar compounds on the walls of the mesofluidic device.

Parallel DNA Synthesis on Poly(ethylene terephthalate)

The fabrication of DNA arrays directly on aminolyzed sheets of poly(ethylene terephthalate) (PET) is described. Array surfaces typically employ bifunctional linkers or layers of covalently attached polymers to provide substrate hydroxy groups as synthesis attachment points. An amine treatment is used here to expose hydroxy groups on films of PET. These hydroxy groups can then be used to couple phosphoramidites and initiate the array synthesis without further functionalization steps. Arrays fabricated on these substrates with a maskless array synthesizer are tolerant of the high number of chemical exposure steps required to synthesize relatively long oligonucleotides. The results might be of the greatest use to the synthetic biology community, for whom a flexible and robust substrate could enable new strategies to enhance the throughput of oligonucleotide synthesis.

Custom 3D printer and resin for 18 μm × 20 μm microfluidic flow channels

While there is great interest in 3D printing for microfluidic device fabrication, to-date the achieved feature sizes have not been in the truly microfluidic regime (<100 μm). In this paper we demonstrate that a custom digital light processor stereolithographic (DLP-SLA) 3D printer and a specifically-designed, low cost, custom resin can readily achieve flow channel cross sections as small as 18 μm × 20 μm. Our 3D printer has a projected image plane resolution of 7.6 μm and uses a 385 nm LED, which dramatically increases the available selection of UV absorbers for resin formulation compared to 3D printers with 405 nm LEDs. Beginning with 20 candidate absorbers, we demonstrate the evaluation criteria and process flow required to develop a high-resolution resin. In doing so, we introduce a new mathematical model for characterizing the resin optical penetration depth based only on measurement of the absorber's molar absorptivity. Our final resin formulation uses 2-nitrophenyl phenyl sulfide (NPS) as the UV absorber. We also develop a novel channel narrowing technique that, together with the new resin and 3D printer resolution, enables small flow channel fabrication. We demonstrate the efficacy of our approach by fabricating 3D serpentine flow channels 41 mm long in a volume of only 0.12 mm3, and by printing high aspect ratio flow channels <25 μm wide and 3 mm tall. These results indicate that 3D printing is finally positioned to challenge the pre-eminence of methods such as soft lithography for microfluidic device prototyping and fabrication.

A new droplet-forming fluidic junction for the generation of highly compartmentalised capsules

A new oscillatory microfluidic junction is described, which enables the consistent formation of highly uniform and complex double emulsions, and is demonstrated for the encapsulation of four different reagents within the inner droplets (called cores) of the double emulsion droplets. Once the double emulsion droplets had attained a spherical form, the cores assumed specific 3D arrangements, the orchestration of which appeared to depend upon the specific emulsion morphology. Such double emulsion droplets were used as templates to produce highly compartmentalised microcapsules and multisomes. Based on these construct models, we numerically demonstrated a model chemical reaction sequence between and within the liquid cores. This work could provide a platform to perform space/time-dependent applications, such as programmed experiments, synthesis, and delivery systems.

3D printing scanning electron microscopy sample holders: A quick and cost effective alternative for custom holder fabrication

A simple and cost effective alternative for fabricating custom Scanning Electron Microscope (SEM) sample holders using 3D printers and conductive polylactic acid filament is presented. The flexibility of the 3D printing process allowed for the fabrication of sample holders with specific features that enable the high-resolution imaging of nanoelectrodes and nanopipettes. The precise value of the inner semi cone angle of the nanopipettes taper was extracted from the acquired images and used for calculating their radius using electrochemical methods. Because of the low electrical resistivity presented by the 3D printed holder, the imaging of non-conductive nanomaterials, such as alumina powder, was found to be possible. The fabrication time for each sample holder was under 30 minutes and the average cost was less than $0.50 per piece. Despite being quick and economical to fabricate, the sample holders were found to be sufficiently resistant, allowing for multiple uses of the same holder.

Moving from millifluidic to truly microfluidic sub-100-μm cross-section 3D printed devices

Three-dimensional (3D) printing has generated considerable excitement in recent years regarding the extensive possibilities of this enabling technology. One area in which 3D printing has potential, not only for positive impact but also for substantial improvement, is microfluidics. To date many researchers have used 3D printers to make fluidic channels directed at point-of-care or lab-on-a-chip applications. Here, we look critically at the cross-sectional sizes of these 3D printed fluidic structures, classifying them as millifluidic (larger than 1 mm), sub-millifluidic (0.5-1.0 mm), large microfluidic (100-500 μm), or truly microfluidic (smaller than 100 μm). Additionally, we provide our prognosis for making 10-100-μm cross-section microfluidic features with custom-formulated resins and stereolithographic printers. Such 3D printed microfluidic devices for bioanalysis will accelerate research through designs that can be easily created and modified, allowing improved assays to be developed.

Generation and manipulation of hydrogel microcapsules by droplet-based microfluidics for mammalian cell culture

Hydrogel microcapsules provide miniaturized and biocompatible niches for three-dimensional (3D) in vitro cell culture. They can be easily generated by droplet-based microfluidics with tunable size, morphology, and biochemical properties. Therefore, microfluidic generation and manipulation of cell-laden microcapsules can be used for 3D cell culture to mimic the in vivo environment towards applications in tissue engineering and high throughput drug screening. In this review of recent advances mainly since 2010, we will first introduce general characteristics of droplet-based microfluidic devices for cell encapsulation with an emphasis on the fluid dynamics of droplet breakup and internal mixing as they directly influence microcapsule's size and structure. We will then discuss two on-chip manipulation strategies: sorting and extraction from oil into aqueous phase, which can be integrated into droplet-based microfluidics and significantly improve the qualities of cell-laden hydrogel microcapsules. Finally, we will review various applications of hydrogel microencapsulation for 3D in vitro culture on cell growth and proliferation, stem cell differentiation, tissue development, and co-culture of different types of cells.

Microfluidic-assisted fabrication of carriers for controlled drug delivery

The microfluidic technique has brought unique opportunities toward the full control over the production processes for drug delivery carriers, owing to the miniaturisation of the fluidic environment. In comparison to the conventional batch methods, the microfluidic setup provides a range of advantages, including the improved controllability of material characteristics, as well as the precisely controlled release profiles of payloads. This review gives an overview of different fluidic principles used in the literature to produce either polymeric microparticles or nanoparticles, focusing on the materials that could have an impact on drug delivery. We also discuss the relations between the particle size and size distribution of the obtained carriers, and the design and configuration of the microfluidic setups. Overall, the use of microfluidic technologies brings exciting opportunities to expand the body of knowledge in the field of controlled drug delivery and great potential to clinical translation of drug delivery systems.

The Use of Microfluidics in Cytotoxicity and Nanotoxicity Experiments

Many unique chemical compounds and nanomaterials are being developed, and each one requires a considerable range of in vitro and/or in vivo toxicity screening in order to evaluate their safety. The current methodology of in vitro toxicological screening on cells is based on well-plate assays that require time-consuming manual handling or expensive automation to gather enough meaningful toxicology data. Cost reduction; access to faster, more comprehensive toxicity data; and a robust platform capable of quantitative testing, will be essential in evaluating the safety of new chemicals and nanomaterials, and, at the same time, in securing the confidence of regulators and end-users. Microfluidic chips offer an alternative platform for toxicity screening that has the potential to transform both the rates and efficiency of nanomaterial testing, as reviewed here. The inherent advantages of microfluidic technologies offer high-throughput screening with small volumes of analytes, parallel analyses, and low-cost fabrication.

3D Printing of Biomolecular Models for Research and Pedagogy

The construction of physical three-dimensional (3D) models of biomolecules can uniquely contribute to the study of the structure-function relationship. 3D structures are most often perceived using the two-dimensional and exclusively visual medium of the computer screen. Converting digital 3D molecular data into real objects enables information to be perceived through an expanded range of human senses, including direct stereoscopic vision, touch, and interaction. Such tangible models facilitate new insights, enable hypothesis testing, and serve as psychological or sensory anchors for conceptual information about the functions of biomolecules. Recent advances in consumer 3D printing technology enable, for the first time, the cost-effective fabrication of high-quality and scientifically accurate models of biomolecules in a variety of molecular representations. However, the optimization of the virtual model and its printing parameters is difficult and time consuming without detailed guidance. Here, we provide a guide on the digital design and physical fabrication of biomolecule models for research and pedagogy using open source or low-cost software and low-cost 3D printers that use fused filament fabrication technology.

Advanced reactor engineering with 3D printing for the continuous-flow synthesis of silver nanoparticles

3D printing has been employed to manufacture advanced reactor geometries based on miniaturised continuous-flow oscillatory baffled reactors (mCOBRs) and they have been applied for the fouling free continuous-flow synthesis of silver nanoparticles with optimal size control.

Fabrication of PDMS microfluidic devices with 3D wax jetting

Network flowing on the 3D PDMS microfluidic chips fabricated with replication of a 3D printed wax mold.

A transparent 3D printed device for assembling droplet hydrogel bilayers (DHBs)

We report a new approach for assembling droplet hydrogel bilayers (DHBs) using a transparent 3D printed device.

Microfluidics platform for glass capillaries and its application in droplet and nanoparticle fabrication

The accessibility to microfluidics of a broader scientific community is often limited by the costly and complex manufacture of the chips. In this respect, we present a simple and reusable platform for the flexible and easy assembly of glass capillaries to create a microfluidics chip within minutes, with excellent chemical compatibility and durability, and without the need of using specialized infrastructure. To demonstrate the application of the proposed platform, we have used it to produce microparticles by the double emulsion approach, nanoparticles by nanoprecipitation, and screened the nanoparticles' size and polydispersity obtained upon modification of various parameters.

Fully inkjet-printed microfluidics: a solution to low-cost rapid three-dimensional microfluidics fabrication with numerous electrical and sensing applications

As the needs for low-cost rapidly-produced microfluidics are growing with the trend of Lab-on-a-Chip and distributed healthcare, the fully inkjet-printing of microfluidics can be a solution to it with numerous potential electrical and sensing applications. Inkjet-printing is an additive manufacturing technique featuring no material waste and a low equipment cost. Moreover, similar to other additive manufacturing techniques, inkjet-printing is easy to learn and has a high fabrication speed, while it offers generally a great planar resolution down to below 20 µm and enables flexible designs due to its inherent thin film deposition capabilities. Due to the thin film feature, the printed objects also usually obtain a high vertical resolution (such as 4.6 µm). This paper introduces a low-cost rapid three-dimensional fabrication process of microfluidics, that relies entirely on an inkjet-printer based single platform and can be implemented directly on top of virtually any substrates.

3D Printed Micro Free-Flow Electrophoresis Device

The cost, time, and restrictions on creative flexibility associated with current fabrication methods present significant challenges in the development and application of microfluidic devices. Additive manufacturing, also referred to as three-dimensional (3D) printing, provides many advantages over existing methods. With 3D printing, devices can be made in a cost-effective manner with the ability to rapidly prototype new designs. We have fabricated a micro free-flow electrophoresis (μFFE) device using a low-cost, consumer-grade 3D printer. Test prints were performed to determine the minimum feature sizes that could be reproducibly produced using 3D printing fabrication. Microfluidic ridges could be fabricated with dimensions as small as 20 μm high × 640 μm wide. Minimum valley dimensions were 30 μm wide × 130 μm wide. An acetone vapor bath was used to smooth acrylonitrile-butadiene-styrene (ABS) surfaces and facilitate bonding of fully enclosed channels. The surfaces of the 3D-printed features were profiled and compared to a similar device fabricated in a glass substrate. Stable stream profiles were obtained in a 3D-printed μFFE device. Separations of fluorescent dyes in the 3D-printed device and its glass counterpart were comparable. A μFFE separation of myoglobin and cytochrome c was also demonstrated on a 3D-printed device. Limits of detection for rhodamine 110 were determined to be 2 and 0.3 nM for the 3D-printed and glass devices, respectively.

Towards Single-Step Biofabrication of Organs on a Chip via 3D Printing

Organ-on-a-chip engineering employs microfabrication of living tissues within microscale fluid channels to create constructs that closely mimic human organs. With the advent of 3D printing, we predict that single-step fabrication of these devices will enable rapid design and cost-effective iterations in the development stage, facilitating rapid innovation in this field.